Field of the Invention
The present invention relates to a frequency division circuit, a method of controlling the frequency division circuit, and an analog electronic timepiece.
Background Art
A frequency division circuit that is used for an analog electronic timepiece includes a monitor terminal from which an output signal of an upper stage frequency division circuit is output to the outside, in an intermediate portion of a frequency division stage, in order to measure the accuracy of a crystal vibrator. In addition, in order to perform a test (acceleration test) of a lower stage frequency division circuit, a signal from the outside is input to the lower stage frequency division circuit through the monitor terminal (refer to FIG. 8).
However, since a signal is input to and output from the same monitor terminal, if noise such as static electricity is input to the monitor terminal from the outside, an operation of the lower stage frequency division circuit is disturbed, and a phenomenon occurs in which time varies or an operation is not performed.
In order to solve the problem, a method in which an input and output function of the monitor terminal is switched by using a signal from another input terminal as a control signal has been disclosed (refer to JP-A-2007-114031).
However, in this method, a control terminal SELECT has to be provided as a new input terminal (refer to FIG. 9). An input terminal of an IC requires not only a pad portion, but also a diode for input protection or a resistor for limiting a current, and an area which is occupied by one terminal affects the entire area of the IC.
In addition, there is a problem in which, although the monitor terminal is used as an output terminal by a newly provided control terminal, if noise such as static electricity is input to the control terminal, the monitor terminal functions as an input terminal, and an operation of the frequency division circuit is disturbed by noise such as static electricity.